High Al heat-resistant alloy steels having Al coating thereon

Abstract

A high-Al heat resistant steel comprising a base steel containing not more than 0.7% C, not more than 3.0% Si, not more than 2.0% Mn, 10 to 40% Ni, 9 to 30% Cr, 2 to 8% Al, with balance being Fe and unavoidable impurities, and an Al coating formed on the base steel. The Al coating diffuses into the base steel to form an intermediate Al alloyed layer during the Al coating or by heating after the coating, which alloyed layer prevents the Al coating from spalling, thus providing excellent resistance to oxidation, corrosion, carburization, nitrization and sulphurdization at elevated temperatures.

What we claim: 
     
       1. A high-Al heat resistant coated steel comprising a base steel consisting essentially of, in weight percent, not more than 0.7% C, not more than 3.0% Si, not more than 2.0% Mn, 10 to 40% Ni, 9 to 30% Cr, 2 to 8% Al, with balance being Fe and unavoidable impurities, and an Al coating formed on the base steel. 
     
     
       2. A high-Al heat resistant coated steel comprising a base steel consisting essentially of, in weight percent, not more than 0.7% C, not more than 3.0% Si, not more than 2.0% Mn, 10 to 40% Ni, 9 to 30% Cr, 2 to 8% Al, with balance being Fe and unavoidable impurities, and a high-Al alloy layer formed on the base steel. 
     
     
       3. A high-Al heat resistant coated steel according to claim 1, in which the Al coating is formed by an Al hot dipping process. 
     
     
       4. A high-Al heat resistant coated steel according to claim 1, in which the aluminum is formed by an electro-aluminum plating process. 
     
     
       5. A high-Al heat resistant coated steel according to claim 1, in which the aluminum coating is formed by a calorizing process. 
     
     
       6. A high-Al heat resistant coated steel according to claim 1, in which the aluminum coating is formed by a metallizing process. 
     
     
       7. A high-Al heat resistant coated steel according to claim 2, in which the high Al alloy coating is formed by heating the high-Al heat resistant steel with the Al coating thereon at a temperature above 500° C. 
     
     
       8. A high-Al heat resistant coated steel according to claim 1, in which the Al coating is 1 to 500 μm in thickness. 
     
     
       9. A high-Al heat resistant coated steel according to claim 1, in which the Al coating is partially alloyed with the base steel. 
     
     
       10. A high-Al heat resistant coated steel according to claim 1 wherein the base steel has the composition 0.078% C, 0.53% Si, 1.54% Mn, 23.2% Ni, 22.4% Cr, 2.10% Al, 0.3% Ti with the balance being Fe and unavoidable impurities. 
     
     
       11. A high-Al heat resistant coated steel according to claim 1 wherein the base steel has the composition 0.15% C, 0.63% Si, 0.74% Mn, 35.3% Ni, 12.0% Cr, 6.79% Al, 0.79% Mo, 0.05% Ce with the balance being Fe and unavoidable impurities. 
     
     
       12. A high-Al heat resistant coated steel according to claim 1 wherein the base steel has the composition 0.45% C, 1.07% Si, 0.53% Mn, 28.3% Ni, 15.2% Cr, 7.58% Al, 0.05% Ce, 0.01% La, 0.001% Ca with the balance being Fe and unavoidable impurities.